1. Field of the Invention
This invention relates to a cover for use with an inflatable modular structure. The inflatable modular structure can be used as a spaced based platform or a habitat for use on a planet or other extraterrestrial body.
2. Description of the Prior Art
Inflatable modular structures are well known in the art as typified, for example, by U.S. Pat. No. 6,439,508 to Taylor, U.S. Pat. No. 6,231,010 to Schneider, et al, and U.S. Pat. No. 6,547,189 to Raboin, et al.
A major advantage to inflatable structures is that while the internal volume of a typical rigid hulled craft does not vary once deployed into space, the opposite is true for the inflatable structure. Once deployed into orbit, or to an extraterrestrial mass, the inside of the inflatable structure is filled with gas or air. The flexible hull, or shell, expands in response to the gas and, as a result, the internal volume of the inflatable structure increases. Thus, the internal volume of an inflated structure having a flexible hull becomes substantially larger than the volume of a solid hulled structure where both structures have a similar launch payload volume.
This fact translates into a significant cost savings. A single inflatable structure can provide an internal volume equivalent to a number of solid hulled structures. With present costs at approximately $10,000.00 to deploy a single pound of payload into space, a single launch of an inflatable module would provide a volume comparable to a number of launches containing rigid hulled structures. Couple this with the fact that many launch payloads can be several tons in weight, it is immediately apparent that a reduced number of launches saves a considerable amount of money.
While inflatable structures offer a number of advantages to less flexible structures, there are, however, technological challenges to deploying an inflatable module. For example, the flexible hull must be collapsible so that the module can fit into payload compartment of a launch vehicle and secured in place as to prevent unwanted effects arising from the acceleration of a launch on an unsecured mass. This is referred to as the pre-deployment configuration and storage of the hull at this stage should be done in a way such that the launch should not damage the hull.
A typical flexible hull has a number of layers. The internal surface is usually composed of an air bladder. The air bladder acts as a barrier to keep gas internal to the module from escaping into space. A typical air bladder is not very thick and to function optimally it cannot have any leaks. When compacted for launch, it is important that the bladder does not come into contact with surfaces that could damage the hull.
An inflatable structure usually has a central core. The core is most often solid and runs the longitudinal length of the module. The core acts as a backbone to the structure and assists in, among other things, providing the shape to the structure and a framework for securing equipment.
To reduce the weight of the module, the core does not take the form of a solid hull. Rather, the core can be comprised of distal ends joined by a number of connecting elements such as longerons. In this form, the core is not designed to cooperate with a collapsed flexible hull. The core could have sharp edges or other protrusions that could damage the bladder of the hull.
At the launch stage, the bladder must be secured about the core in such a way as to minimize the opportunity for perforations, punctures, and tears in the bladder. One way to reduce the chance of damaging the bladder is to place a relatively smooth surface on the outside of the core so that the flexible hull could be folded around the surface without making contact with the core. The relatively smooth surface would be connected to the core and substantially surround the core to provide protection and support for the bladder. This surface could be part of a cover that is adapted to work with the core.
Another issue concerning the flexible hull is the use of windows. It is not unusual for a structure to have at least one window if not more integral to the flexible hull. As a flexible hull is usually comprised of a number of layers including, but not limited to, an orbital debris shield, a restraint layer, and a bladder, there must be an opening through each layer for viewing through the window. Furthermore, the window would be secured to at least one layer of the hull. When collapsing the hull for the launch configuration, care must be taken to insure that the window is properly indexed in relation to the rest of the hull (thereby minimizing the tension between the window and hull while collapsing the hull) and that the window does not break due to the forces exerted on the smooth surface of the cover.
This could be accomplished in a number of ways. The smooth surface of the cover can be partially flexible to bend to a degree rather than being rigid. Also, a buffer material such as rubber can be placed between the window and the smooth surface. As to properly indexing the window in relation to the rest of the hull, the smooth surface may have an access port, opening, or a hingable structure such as a door. The opening can be used to insure that the window is in the correct location and then the opening closed to provide a further degree of support.
One potential drawback to this approach arises due to the fact that the cover would restrict access from the core to the internal volume of the structure when the hull becomes inflated. Thus, whatever form the cover takes, it must be removable from the core to allow access to the full internal volume created by the hull when the module is deployed.
Another challenge lies in the characteristic of the internal surface of the flexible hull. While a rigid hull can function to secure equipment to the inside of a solid hull, the inside of the flexible hull is not so functional. Typically, the bladder forms the inside surface of an inflatable structure. The bladder does not have the structural qualities of a solid hull.
While the micro-gravity condition in space does not require the bladder to support the full weight of an item that may be attached to the surface of the bladder, nevertheless whatever comes into contact with the bladder might experience forces from other sources that could damage the bladder. One answer to this problem would be to secure a large panel to the inside surface of the bladder that conforms to the surface of the bladder and can support equipment without the equipment coming into contact with the bladder. The panel would serve to protect the bladder from contact with potentially damaging items and provide a foundation for securing items, such as equipment, in place.
Yet another challenge exists in the storage of materials and equipment at launch. While an inflatable module usually has a solid core, this does not mean that the core alone can function to store all the items needed in the structure. Furthermore, it may be necessary to distribute the weight at launch such that the core would not be an optimum place to contain storage items.
What is needed is a cover to provide a smooth surface for folding the bladder and flexible hull in the pre-deployed configuration. The cover would be substantially hollow for storing items prior to launch and during a mission. Further, the cover would be removable from the core after launch and during deployment. Finally, the surface of the cover would be contoured to conform to the inside surface of the bladder and securable to the bladder to protect the bladder and to act as a foundation for securing equipment, materials, or other items as needed.